Electrolyte for lithium secondary battery and lithium secondary battery using the same

ABSTRACT

An electrolyte for a lithium secondary battery, the electrolyte including: a lithium salt; a non-aqueous organic solvent; and a piperazine derivative represented by Formula 1 having an oxidation potential lower than an oxidation potential of the non-aqueous organic solvent by about 2 V to about 4 V: 
                         
wherein, in Formula 1, X, Y, and R 1  to R 4  are defined in the specification.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority to Korean Patent Application No.10-2013-0104501, filed on Aug. 30, 2013, and all the benefits accruingtherefrom under 35 U.S.C. §119, the content of which is incorporatedherein in its entirety by reference.

BACKGROUND

1. Field

The present disclosure relates to an electrolyte for a lithium secondarybattery, and a lithium secondary battery including the electrolyte.

2. Description of the Related Art

Lithium ions batteries (“LIBs”) possess high energy density per unitweight and can be easily designed. Thus, these batteries have beendeveloped for use in small electronic and portable IT devices. In recentyears, small and medium sized lithium ion batteries have drawn attentionas suitable power sources for electric vehicles and power storagedevices storing electricity produced as an alternate.

A lithium secondary battery includes a cathode, an anode, and aseparator. During discharging of the lithium secondary battery,oxidation reaction occurs in the anode due to deintercalation of lithiumions, while reduction reaction occurs in the cathode due tointercalation of lithium ions. The vice versa processes take placeduring the battery charging. The electrolyte has conductivity only forions, not for electrons, and thus transfers lithium ions between thecathode and the anode.

Lithium ions intercalated into an electrode of a battery lead to chargeneutrality with electrons entered into the electrode, and thus serve asmedia storing electric energy in the electrode. Accordingly, thequantity of electric energy storable by the battery is dependent uponthe quantity of lithium ions intercalated into the electrode to createthe charge neutrality. Although basic performance of the lithiumsecondary battery, such as operating voltage and energy density, isdependent upon the materials of the cathode and anode, the electrolytealso needs to have high-ion conductivity, electrochemical stability andthermal stability to ensure high performance of the lithium secondarybattery.

A typical lithium ion battery electrolyte consists of a lithium salt andan organic solvent. The electrolyte needs to be electrochemically stablein a voltage range where reduction and oxidation proceed in the anodeand cathode, respectively.

As the use of lithium secondary batteries is expanding to electricvehicles and power storage fields, electrode active materials for use athigh voltages emerged and became available. Use of a relativelylow-potential anode active material and a relatively high-potentialcathode active material has led to a narrower potential window of theelectrolyte, so that the electrolyte is more likely to decompose on asurface of the cathode/anode. Lithium secondary batteries for electricvehicles and power storage are likely to be exposed to externalhigh-temperature environment conditions, and the temperatures of theselithium secondary batteries may rise during instantaneous charging anddischarging. Accordingly, lifetime and stored energy quantity of thelithium secondary battery may be reduced in such high-temperatureenvironment conditions.

Therefore, there remains a demand for the development of an electrolytecomposition which would provide improved lifetime and high-ratecharacteristics of the lithium secondary batteries.

SUMMARY

Provided is an electrolyte for a lithium secondary battery that isresistant to oxidation on a surface of cathode, and that providesimproved lifetime characteristics and high-rate characteristics.

Provided is a lithium secondary battery with improved lifetimecharacteristics and high-rate characteristics, the lithium secondarybattery including the electrolyte.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect of the present disclosure, an electrolyte for alithium secondary battery includes:

a lithium salt;

a non-aqueous organic solvent; and

a piperazine derivative represented by Formula 1 having an oxidationpotential lower than an oxidation potential of the non-aqueous organicsolvent by about 2 V to about 4 V:

wherein, in Formula 1,

at least one of X and Y is selected from a C₁-C₆₀ alkyl group, a C₁-C₆₀aminoalkyl group, a C₁-C₆₀ thioalkyl group, a C₁-C₆₀ hydroxyalkyl group,a C₁-C₆₀ alkylnitrile group, and a substituted or unsubstituted C₆-C₆₀aryl group, and the unselected rest of X and Y is a hydrogen atom;

R₁ to R₄ are each independently selected from a hydrogen atom, adeuterium atom, a halogen atom, a hydroxyl group, a cyano group, a nitrogroup, an azido group, an amino group, an amido group, an amidino group,a hydrazine group, a hydrazone group, a carboxyl group or a saltthereof, a sulfonic acid group or a salt thereof, a phosphoric acidgroup or a salt thereof, a thiol group, —C(═O)—H, a substituted orunsubstituted C₁-C₆₀ alkyl group, a substituted or unsubstituted C₁-C₆₀alkoxy group, a substituted or unsubstituted C₁-C₆₀ heteroalkyl group, asubstituted or unsubstituted C₂-C₆₀ alkenyl group, a substituted orunsubstituted C₂-C₆₀ alkynyl group, a substituted or unsubstitutedC₃-C₁₀ cycloalkyl group, a substituted or unsubstituted C₃-C₁₀heterocycloalkyl group, a substituted or unsubstituted C₂-C₁₀cycloalkenyl group, a substituted or unsubstituted C₂-C₁₀heterocycloalkenyl group, a substituted or unsubstituted C₆-C₆₀ arylgroup, a substituted or unsubstituted C₆-C₆₀ aryloxy group, asubstituted or unsubstituted C₂-C₆₀ heteroaryl group,-(Q₁)_(r)-(Q₂)_(s), —N(Q₃)(Q₄)(Q₅), —P(═O)(Q₆)(Q₇), and—P(Q₈)(Q₉)(Q₁₀)(Q₁₁);

wherein at least one of R₁₁ to R₁₄ and at least one of R₂₁ to R₃₀ areoptionally linked to each other to form a substituted or unsubstituted,saturated or unsaturated ring;

Q₁ is at least one selected from —O—, —S—, —C(═O)—, a substituted orunsubstituted C₁-C₆₀ alkylene group, a substituted or unsubstitutedC₂-C₆₀ alkenylene group, a substituted or unsubstituted C₃-C₁₀cycloalkylene group, a substituted or unsubstituted C₃-C₁₀heterocycloalkylene group, a substituted or unsubstituted C₂-C₁₀cycloalkenylene group, a substituted or unsubstituted C₂-C₁₀heterocycloalkenylene group, a substituted or unsubstituted C₆-C₆₀arylene group, and a substituted or unsubstituted C₂-C₆₀ heteroarylenegroup;

Q₂ to Q₁₁ are each independently selected from a deuterium atom, ahalogen atom, a hydroxyl group, a cyano group, a nitro group, an azidogroup, an amino group, an amido group, an amidino group, a hydrazinegroup, a hydrazone group, a carboxyl group or a salt thereof, a sulfonicacid group or a salt thereof, a phosphoric acid group or a salt thereof,a thiol group, a substituted or unsubstituted C₁-C₆₀ alkyl group, asubstituted or unsubstituted C₁-C₆₀ alkoxy group, a substituted orunsubstituted C₁-C₆₀ heteroalkyl group, a substituted or unsubstitutedC₂-C₆₀ alkenyl group, a substituted or unsubstituted C₂-C₆₀ alkynylgroup, a substituted or unsubstituted C₁-C₆₀ alkoxy group, a substitutedor unsubstituted C₃-C₁₀ cycloalkyl group, a substituted or unsubstitutedC₃-C₁₀ heterocycloalkyl group, a substituted or unsubstituted C₂-C₁₀cycloalkenyl group, a substituted or unsubstituted C₂-C₁₀heterocycloalkenyl group, a substituted or unsubstituted C₆-C₆₀ arylgroup, a substituted or unsubstituted C₆-C₆₀ aryloxy group, and asubstituted or unsubstituted C₂-C₆₀ heteroaryl group; and

r and s are each independently an integer from 1 to 5, wherein,

when r is 2 or greater, groups Q₁ are each identical to or differentfrom each other, and

when s is 2 or greater, groups Q₂ are each identical to or differentfrom each other.

According to another aspect of the present disclosure, a lithiumsecondary battery includes:

-   a cathode,-   an anode, and

the electrolyte described above disposed between the cathode and theanode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view illustrating a thin filmformed on a surface of a cathode of a lithium secondary batteryaccording to an embodiment;

FIG. 2 is an exploded perspective view of a lithium secondary batteryaccording to an embodiment;

FIG. 3 is a graph of discharge capacity (milliAmpere×hour per gram,mA×h/g) versus cycle number showing discharge capacities of the lithiumsecondary batteries of Examples 1-2 and Comparative Examples 1-4;

FIG. 4 is a diagram of charge/discharge efficiencies of the lithiumsecondary batteries of Examples 1-2 and Comparative Examples 1-2;

FIG. 5 is a graph of discharge capacity (milliAmpere×hour per gram,mA×h/g) versus cycle number showing high-rate characteristics of thelithium secondary batteries of Examples 1-4 and Comparative Examples1-4; and

FIGS. 6A to 6C are graphs of intensity (arbitrary units, a. u.) versusbinding energy (electron Volt, eV) illustrating X-ray photoelectronspectra of cathode surface material from the lithium secondary batteriesof Examples 1-2 and Comparative Examples 1 and 2 after 300^(th) chargeand discharge cycle.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to the like elements throughout. In this regard, thepresent embodiments may have different forms and should not be construedas being limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items. Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list.

It will be understood that when an element is referred to as being “on”another element, it can be directly in contact with the other element orintervening elements may be present therebetween. In contrast, when anelement is referred to as being “directly on” another element, there areno intervening elements present.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers, and/or sections, these elements, components, regions, layers,and/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer, orsection from another element, component, region, layer, or section.Thus, a first element, component, region, layer, or section discussedbelow could be termed a second element, component, region, layer, orsection without departing from the teachings of the present embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise.

The term “or” means “and/or.” It will be further understood that theterms “comprises” and/or “comprising,” or “includes” and/or “including”when used in this specification, specify the presence of statedfeatures, regions, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, regions, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this general inventive conceptbelongs. It will be further understood that terms, such as those definedin commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand the present disclosure, and will not be interpreted in an idealizedor overly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

As used herein, the term “alkyl” indicates a group derived from acompletely saturated, branched or unbranched (or a straight or linear)hydrocarbon. Non-limiting examples of the “alkyl” group include methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl,iso-pentyl, neo-pentyl, iso-amyl, n-hexyl, 3-methylhexyl,2,2-dimethylpentyl, 2,3-dimethylpentyl, and n-heptyl.

As used herein, the term “heteroalkyl” group indicates an alkyl groupthat comprises at least one heteroatom covalently bonded to one or morecarbon atoms of the alkyl group. Each heteroatom is independently chosenfrom nitrogen (N), oxygen (O), sulfur (S), and phosphorus (P).Non-limiting examples of the “heteroalkyl” group include methoxymethyland 2-methoxyethyl.

As used herein, the term “cycloalkyl” indicates a group having one ormore saturated rings in which all ring members are carbon. Non-limitingexamples of the “cycloalkyl” group include cyclopentyl and cyclohexyl.

As used herein, the term “heterocycloalkyl” group indicates an alkylgroup that comprises at least one heteroatom covalently bonded to one ormore carbon atoms of the cycloalkyl group. Each heteroatom isindependently chosen from nitrogen (N), oxygen (O), sulfur (S), andphosphorus (P). Non-limiting examples of the “heterocycloalkyl” groupinclude 2-tetrahydrofuranyl and 2-tetrahydropyranyl.

As used herein, the term “halogen atom” indicates fluorine, bromine,chloride, iodine, and the like.

As used herein, the term “alkoxy” represents “alkyl-O—”, wherein theterm “alkyl” has the same meaning as described above. Non-limitingexamples of the alkoxy group are methoxy, ethoxy, propoxy, 2-propoxy,n-butoxy, sec-butoxy, t-butoxy, pentyloxy, hexyloxy, cyclopropoxy, andcyclohexyloxy.

As used herein, the term “alkenyl” indicates a group derived from abranched or unbranched hydrocarbon with at least one carbon-carbondouble bond. Non-limiting examples of the alkenyl group include vinyl,n-propenyl, n-butenyl, iso-propenyl, and iso-butenyl.

As used herein, the term “alkynyl” indicated a group derived from abranched or unbranched hydrocarbon with at least one carbon-carbontriple bond. Non-limiting examples of the “alkynyl” group includeethynyl, n-propynyl, n-butynyl, iso-butynyl, and iso-propynyl.

As used herein, the term “cycloalkenyl” indicates a group derived from abranched or unbranched cyclic hydrocarbon with at least onecarbon-carbon double bond inside the cyclic moiety. Non-limitingexamples of the cycloalkenyl group include 1-cyclopentenyl and1-cyclohexenyl.

As used herein, the term “cycloalkynyl” indicates a group derived from abranched or unbranched cyclic hydrocarbon with at least onecarbon-carbon triple bond inside the cyclic moiety. Non-limitingexamples of the cycloalkynyl group include 1-cyclooctynyl and1-cyclononynyl.

As used herein, the term “aryl” group, which is used alone or incombination, indicates an aromatic hydrocarbon containing at least onering. The term “aryl” is construed as including a group with an aromaticring fused to at least one cycloalkyl ring. Non-limiting examples of the“aryl” group are phenyl, naphthyl, and tetrahydronaphthyl.

As used herein, the term “aryloxy” indicates “—O-aryl”. A non-limitingexample of the “aryloxy” group is phenoxy.

As used herein, the term “heteroaryl group” indicates a monocyclic orbicyclic organic compound including at least one heteroatom selectedfrom nitrogen (N), oxygen (O), phosphorous (P), and sulfur (S), whereinthe rest of the cyclic atoms are all carbon.

The heteroaryl group may include, for example, one to five heteroatoms,and in some embodiments, may include a five- to ten-membered ring. Inthe heteroaryl group, S or N may be present in various oxidized forms.Non-limiting examples of the monocyclic heteroaryl group are thienyl,furyl, pyrrolyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl,1,2,3-oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl,1,3,4-oxadiaxolyl, 1,2,3-thiadiazolyl, 1,2,4-thiadiazolyl,1,2,5-thiadiazolyl, 1,3,4-thiazolyl, isothiazol-3-yl, isothiazol-4-yl,isothiazol-5-yl, oxazol-2-yl, oxazol-4-yl, oxazol-5-yl, isoxazol-3-yl,isoxazol-4-yl, isoxazol-5-yl, 1,2,4-triazol-3-yl, 1,2,4-triazol-5-yl,1,2,3-triazol-4-yl, 1,2,3-triazol-5-yl, tetrazolyl, pyrid-2-yl,pyrid-3-yl, 2-pyrazin-2-yl, pyrazin-4-yl, pyrazin-5-yl,2-pyrimidin-2-yl, 4-pyrimidin-2-yl, and 5-pyrimidin-2-yl.

As used herein, the term “heteroaryl” indicates a heteroaromatic ringfused to at least one of an aryl group, a cycloaliphatic group, and aheterocyclic group. Non-limiting examples of the bicyclic heteroarylgroup are indolyl, isoindolyl, indazolyl, indolizinyl, purinyl,quinolizinyl, quinolinyl, isoquinolinyl, cinnolinyl, phthalazinyl,naphthyridinyl, quinazolinyl, quinaxalinyl, phenanthridinyl,phenathrolinyl, phenazinyl, phenothiazinyl, phenoxazinyl,benzisoqinolinyl, thieno[2,3-b]furanyl, furo[3,2-b]-pyranyl,5H-pyrido[2,3-d]-o-oxazinyl, 1 H-pyrazolo[4,3-d]-oxazolyl,4H-imidazo[4,5-d]thiazolyl, pyrazino[2,3-d]pyridazinyl,imidazo[2,1-b]thiazolyl, imidazo[1,2-b][1,2,4]triazinyl,7-benzo[b]thienyl, benzoxazolyl, benzimidazolyl, benzothiazolyl,benzoxapinyl, benzoxazinyl, 1H-pyrrolo[1,2-b][2]benzazapinyl,benzofuryl, benzothiophenyl, benzotriazolyl, pyrrolo[2,3-b]pyridinyl,pyrrolo[3,2-c]pyridinyl, pyrrolo[3,2-b]pyridinyl,imidazo[4,5-b]pyridinyl, imidazo[4,5-c]pyridinyl,pyrazolo[4,3-d]pyridinyl, pyrazolo[4,3-c]pyridinyl,pyrazolo[3,4-c]pyridinyl, pyrazolo[3,4-d]pyridinyl,pyrazolo[3,4-b]pyridinyl, imidazo[1,2-a]pyridinyl,pyrazolo[1,5-a]pyridinyl, pyrrolo[1,2-b]pyridazinyl,imidazo[1,2-c]pyrimidinyl, pyrido[3,2-d]pyrimidinyl,pyrido[4,3-d]pyrimidinyl, pyrido[3,4-d]pyrimidinyl,pyrido[2,3-d]pyrimidinyl, pyrido[2,3-b]pyrazinyl,pyrido[3,4-b]pyrazinyl, pyrimido[5,4-d]pyrimidinyl,pyrazino[2,3-b]pyrazinyl, and pyrimido[4,5-d]pyrimidinyl.

As used herein, the terms “alkylene”, “alkenylene”, “cycloalkylene”,“heterocycloalkylene”, “cycloalkenylene”, “heterocycloalkenylene”,“arylene”, and “heteroarylene” indicate divalent groups respectivelyderived from “alkyl”, “alkenyl”, “cycloalkyl”, “heterocycloalkyl”,“cycloalkenyl”, “heterocycloalkenyl”, “aryl”, and “heteroaryl” groups.

According to an embodiment of the present disclosure, an electrolyte fora lithium secondary battery includes:

-   a lithium salt;-   a non-aqueous organic solvent; and

a piperazine derivative having an oxidation potential lower than anoxidation potential of the non-aqueous organic solvent by about 2 V toabout 4 V.

The piperazine derivative may include a compound represented by Formula1 below.

In Formula 1 above,

at least one of X and Y may be selected from a C₁-C₆₀ alkyl group, aC₁-C₆₀ aminoalkyl group, a C₁-C₆₀ thioalkyl group, a C₁-C₆₀ hydroxyalkylgroup, a C₁-C₆₀ alkylnitrile group, and a substituted or unsubstitutedC₆-C₆₀ aryl group, and unselected rest of X and Y is a hydrogen atom;

R₁ to R₄ may be each independently selected from a hydrogen atom, adeuterium atom, a halogen atom, a hydroxyl group (—OH), a cyano group(—CN), a nitro group (—NO₂), an azido group (—N₃), an amino group(—NRR′, wherein R and R′ are independently hydrogen or a C₁-C₁₀ alkylgroup), an amido group (—C(═O)NRR′, wherein R and R′ are independentlyhydrogen or a C₁-C₁₀ alkyl group), an amidino group (—C(═NH)NRR′,wherein R and R′ are independently hydrogen or a C₁-C₁₀ alkyl group), ahydrazine group (—NHNRR′, wherein R and R′ are independently hydrogen ora C₁-C₁₀ alkyl group), a hydrazone group (—CR═NHNR′R″, wherein R, R′ andR″ are independently hydrogen or a C₁-C₁₀ alkyl group), a carboxyl group(—CO₂H) or a salt thereof, a sulfonic acid group (—SO₃H) or a saltthereof, a phosphoric acid group (—P(═O)(OH)₂) or a salt thereof, athiol group (—SH), —C(═O)—H, a substituted or unsubstituted C₁-C₆₀ alkylgroup, a substituted or unsubstituted C₁-C₆₀ alkoxy group, a substitutedor unsubstituted C₁-C₆₀ heteroalkyl group, a substituted orunsubstituted C₂-C₆₀ alkenyl group, a substituted or unsubstitutedC₂-C₆₀ alkynyl group, a substituted or unsubstituted C₃-C₁₀ cycloalkylgroup, a substituted or unsubstituted C₃-C₁₀ heterocycloalkyl group, asubstituted or unsubstituted C₂-C₁₀ cycloalkenyl group, a substituted orunsubstituted C₂-C₁₀ heterocycloalkenyl group, a substituted orunsubstituted C₆-C₆₀ aryl group, a substituted or unsubstituted C₆-C₆₀aryloxy group, a substituted or unsubstituted C₂-C₆₀ heteroaryl group,-(Q₁)_(r)-(Q₂)_(s), —N(Q₃)(Q₄)(Q₅), —P(═O)(Q₆)(Q₇), and—P(Q₈)(Q₉)(Q₁₀)(Q₁₁), wherein

Q₁ may be selected from —O—, —S—, —C(═O)—, a substituted orunsubstituted C₁-C₆₀ alkylene group, a substituted or unsubstitutedC₂-C₆₀ alkenylene group, a substituted or unsubstituted C₃-C₁₀cycloalkylene group, a substituted or unsubstituted C₃-C₁₀heterocycloalkylene group, a substituted or unsubstituted C₂-C₁₀cycloalkenylene group, a substituted or unsubstituted C₂-C₁₀heterocycloalkenylene group, a substituted or unsubstituted C₆-C₆₀arylene group, and a substituted or unsubstituted C₂-C₆₀ heteroarylenegroup;

Q₂ to Q₁₁ may be each independently selected from a deuterium atom, ahalogen atom, a hydroxyl group (—OH), a cyano group (—CN), a nitro group(—NO₂), an azido group (—N₃), an amino group (—NRR′, wherein R and R′are independently hydrogen or a C₁-C₁₀ alkyl group), an amido group(—C(═O)NRR′, wherein R and R′ are independently hydrogen or a C₁-C₁₀alkyl group), an amidino group (—C(═NH)NRR′, wherein R and R′ areindependently hydrogen or a C₁-C₁₀ alkyl group), a hydrazine group(—NHNRR′, wherein R and R′ are independently hydrogen or a C₁-C₁₀ alkylgroup), a hydrazone group (—CR═NHNR′R″, wherein R, R′ and R″ areindependently hydrogen or a C₁-C₁₀ alkyl group), a carboxyl group(—CO₂H) or a salt thereof, a sulfonic acid group (—SO₃H) or a saltthereof, a phosphoric acid group (—P(═O)(OH)₂) or a salt thereof, athiol group (—SH), a substituted or unsubstituted C₁-C₆₀ alkyl group, asubstituted or unsubstituted C₁-C₆₀ alkoxy group, a substituted orunsubstituted C₁-C₆₀ heteroalkyl group, a substituted or unsubstitutedC₂-C₆₀ alkenyl group, a substituted or unsubstituted C₂-C₆₀ alkynylgroup, a substituted or unsubstituted C₁-C₆₀ alkoxy group, a substitutedor unsubstituted C₃-C₁₀ cycloalkyl group, a substituted or unsubstitutedC₃-C₁₀ heterocycloalkyl group, a substituted or unsubstituted C₂-C₁₀cycloalkenyl group, a substituted or unsubstituted C₂-C₁₀heterocycloalkenyl group, a substituted or unsubstituted C₆-C₆₀ arylgroup, a substituted or unsubstituted C₆-C₆₀ aryloxy group, and asubstituted or unsubstituted C₂-C₆₀ heteroaryl group; and

r and s may be each independently an integer from 1 to 5.

When r is 2 or greater, group Q₁ may each be identical to or differentfrom each other. When s is 2 or greater, group Q₂ may each be identicalto or different from each other.

In some embodiments, in Formula 1,

R₁ to R₄ may be each independently selected from a hydrogen atom, adeuterium atom, a halogen atom, a hydroxyl group (—OH), a cyano group(—CN), a nitro group (—NO₂), an azido group (—N₃), an amino group(—NRR′, wherein R and R′ are independently hydrogen or a C₁-C₁₀ alkylgroup), an amido group (—C(═O)NRR′, wherein R and R′ are independentlyhydrogen or a C₁-C₁₀ alkyl group), an amidino group (—C(═NH)NRR′,wherein R and R′ are independently hydrogen or a C₁-C₁₀ alkyl group), ahydrazine group (—NHNRR′, wherein R and R′ are independently hydrogen ora C₁-C₁₀ alkyl group), a hydrazone group (—CR═NHNR′R″, wherein R, R′ andR″ are independently hydrogen or a C₁-C₁₀ alkyl group), a carboxyl group(—CO₂H) or a salt thereof, a sulfonic acid group (—SO₃H) or a saltthereof, a phosphoric acid group (—P(═O)(OH)₂) or a salt thereof, athiol group (—SH), —C(═O)—H, a methyl group, an ethyl group, an n-propylgroup, an isopropyl group, an n-butyl group, an isobutyl group, a sec- abutyl group, a tert-butyl group, an n-pentyl group, an isopentyl group,a sec-pentyl group, a tert-pentyl group, an n-hexyl group, an isohexylgroup, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, anisoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octylgroup, an isooctyl group, a sec-octyl group, a tert-octyl group, ann-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group,an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decylgroup, and -(Q₁)_(r)-(Q₂)_(s), wherein

Q₁ may be selected from —O—, —S—, —C(═O)—, a C₁-C₁₀ alkylene group, aC₆-C₁₄ arylene group, and a C₂-C₁₄ heteroarylene group;

Q₂ may be selected from a deuterium atom, a halogen atom, a hydroxylgroup (—OH), a cyano group, a nitro group, an azido group, an aminogroup, an amido group, an amidino group, a hydrazine group, a hydrazonegroup, a carboxyl group or a salt thereof, a sulfonic acid group or asalt thereof, a phosphoric acid group or a salt thereof, a thiol group(—SH), —C(═O)—H, a methyl group, an ethyl group, an n-propyl group, anisopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group,a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentylgroup, a tert-pentyl group, an n-hexyl group, an isohexyl group, asec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptylgroup, a sec-heptyl group, a tert-heptyl group, an n-octyl group, anisooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group,an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decylgroup, an isodecyl group, a sec-decyl group, a tert-decyl group, and aC₁-C₁₀ alkoxy group, and

r and s may each independently be an integer from 1 to 5 wherein,

when r is 2 or greater, groups Q₁ are each identical to or differentfrom each other, and

when s is 2 or greater, groups Q₂ are each identical to or differentfrom each other, but are not limited thereto.

In some other embodiments, in Formula 1,

R₁ to R₄ may be each independently selected from a hydrogen atom, adeuterium atom, a halogen atom, a hydroxyl group (—OH), a cyano group(—CN), a nitro group (—NO₂), an azido group (—N₃), an amino group(—NRR′, wherein R and R′ are independently hydrogen or a C₁-C₁₀ alkylgroup), an amido group (—C(═O)NRR′, wherein R and R′ are independentlyhydrogen or a C₁-C₁₀ alkyl group), an amidino group (—C(═NH)NRR′,wherein R and R′ are independently hydrogen or a C₁-C₁₀ alkyl group), ahydrazine group (—NHNRR′, wherein R and R′ are independently hydrogen ora C₁-C₁₀ alkyl group), a hydrazone group (—CR═NHNR′R″, wherein R, R′ andR″ are independently hydrogen or a C₁-C₁₀ alkyl group), a carboxyl group(—CO₂H) or a salt thereof, a sulfonic acid group (—SO₃H) or a saltthereof, a phosphoric acid group (—P(═O)(OH)₂) or a salt thereof, a thiogroup (—SH), —C(═O)—H, a methyl group, an ethyl group, an n-propylgroup, an isopropyl group, an n-butyl group, an isobutyl group, asec-butyl group, a tert-butyl group, an n-pentyl group, an isopentylgroup, a sec-pentyl group, a tert-pentyl group, an n-hexyl group, anisohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptylgroup, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, ann-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group,an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonylgroup, a n-decyl group, an isodecyl group, a sec-decyl group, atert-decyl group, and the groups represented by Formulae 3A and 3B, butare not limited thereto:

In Formulae 3A and 3B,

Q_(1a) may be a C₁-C₁₀ alkylene group;

Q₂ may be selected from a deuterium atom, a halogen atom, a hydroxylgroup (—OH), a cyano group (—CN), a nitro group (—NO₂), an azido group(—N₃), an amino group (—NRR′, wherein R and R′ are independentlyhydrogen or a C₁-C₁₀ alkyl group), an amido group (—C(═O)NRR′, wherein Rand R′ are independently hydrogen or a C₁-C₁₀ alkyl group), an amidinogroup (—C(═NH)NRR′, wherein R and R′ are independently hydrogen or aC₁-C₁₀ alkyl group), a hydrazine group (—NHNRR′, wherein R and R′ areindependently hydrogen or a C₁-C₁₀ alkyl group), a hydrazone group(—CR═NHNR′R″, wherein R, R′ and R″ are independently hydrogen or aC₁-C₁₀ alkyl group), a carboxyl group (—CO₂H) or a salt thereof, asulfonic acid group (—SO₃H) or a salt thereof, a phosphoric acid group(—P(═O)(OH)₂) or a salt thereof, a thiol group (—SH), —C(═O)—H, a methylgroup, an ethyl group, an n-propyl group, an isopropyl group, an n-butylgroup, an isobutyl group, a sec-butyl group, a tert-butyl group, ann-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentylgroup, an n-hexyl group, an isohexyl group, a sec-hexyl group, atert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptylgroup, a tert-heptyl group, an n-octyl group, an isooctyl group, asec-octyl group, a tert-octyl group, an n-nonyl group, an isononylgroup, a sec-nonyl group, a tert-nonyl group, an n-decyl group, anisodecyl group, a sec-decyl group, a tert-decyl group, and a C₁-C₁₀alkoxy group; and

s may be an integer of 1, 2, or 3.

In some embodiments, the piperazine derivative may be a compoundrepresented by Formula 2 below.

In Formula 2,

at least one of X′ and Y′ may be selected from a C₁-C₁₀ hydroxyalkylgroup, a C₁-C₁₀ oaminoalkyl group, a C₁-C₁₀ alkylnitrile group, and asubstituted or unsubstituted C₁-C₁₀ aryl group, and the unselected restof X′ and Y′ is a hydrogen atom; and

R₁ to R₄ may be each independently selected from a hydrogen atom, adeuterium atom, a halogen atom, a hydroxyl group (—OH), a cyano group, anitro group, an azido group, an amino group, an amido group, an amidinogroup, a hydrazine group, a hydrazone group, a carboxyl group or a saltthereof, a sulfonic acid group or a salt thereof, a phosphoric acidgroup or a salt thereof, a thiol group (—SH), —C(═O)—H, a methyl group,an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group,an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentylgroup, an isopentyl group, a sec-pentyl group, a tert-pentyl group, ann-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group,an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptylgroup, an n-octyl group, an isooctyl group, a sec-octyl group, atert-octyl group, an n-nonyl group, an isononyl group, a sec-nonylgroup, a tert-nonyl group, an n-decyl group, an isodecyl group, asec-decyl group, a tert-decyl group, and -(Q₁)_(r)-(Q₂)_(s), wherein

Q₁ may be selected from —O—, —S—, —C(═O)—, a C₁-C₁₀ alkylene group, aC₆-C₁₄ arylene group, and a C₂-C₁₄ heteroarylene group;

Q₂ may be selected from a deuterium atom, a halogen atom, a hydroxylgroup, a cyano group (—CN), a nitro group (—NO₂), an azido group (—N₃),an amino group (—NRR′, wherein R and R′ are independently hydrogen or aC₁-C₁₀ alkyl group), an amido group (—C(═O)NRR′, wherein R and R′ areindependently hydrogen or a C₁-C₁₀ alkyl group), an amidino group(—C(═NH)NRR′, wherein R and R′ are independently hydrogen or a C₁-C₁₀alkyl group), a hydrazine group (—NHNRR′, wherein R and R′ areindependently hydrogen or a C₁-C₁₀ alkyl group), a hydrazone group(—CR═NHNR′R″, wherein R, R′ and R″ are independently hydrogen or aC₁-C₁₀ alkyl group), a carboxyl group (—CO₂H) or a salt thereof, asulfonic acid group (—SO₃H) or a salt thereof, a phosphoric acid group(—P(═O)(OH)₂) or a salt thereof, a thiol group, —C(═O)—H, a methylgroup, an ethyl group, an n-propyl group, an isopropyl group, an n-butylgroup, an isobutyl group, a sec-a butyl group, a tert-butyl group, an-pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentylgroup, a n-hexyl group, an isohexyl group, a sec-hexyl group, atert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptylgroup, a tert-heptyl group, an n-octyl group, an isooctyl group, asec-octyl group, a tert-octyl group, an n-nonyl group, an isononylgroup, a sec-nonyl group, a tert-nonyl group, an n-decyl group, anisodecyl group, a sec-decyl group, a tert-decyl group, and a C₁-C₁₀alkoxy group, and

r and s may each independently be an integer from 1 to 5 wherein,

when r is 2 or greater, groups Q₁ are each identical to or differentfrom each other, and

when s is 2 or greater, groups Q₂ are each identical to or differentfrom each other, but are not limited thereto.

In some embodiments, the piperazine derivative of Formula 1 may includeat least one of compounds represented by Formulae 3 to 6 below, but isnot limited thereto.

As used herein, with regard to the term “a substituted orunsubstituted”, “substituted” means substitution with a halogen atom, aC₁-C₁₀ alkyl group substituted with a halogen atom (for example, CF₃,CHF₂, CH₂F, CCl₃, or the like), a C₁-C₁₀ alkoxy group, a hydroxyl group(—OH), a nitro group (—NO₂), an azido group (—N₃), a cyano group (—CN),an amino group (—NRR′, wherein R and R′ are independently hydrogen or aC₁-C₁₀ alkyl group), an amido group (—C(═O)NRR′, wherein R and R′ areindependently hydrogen or a C₁-C₁₀ alkyl group), an amidino group(—C(═NH)NRR′, wherein R and R′ are independently hydrogen or a C₁-C₁₀alkyl group), a hydrazine group (—NHNRR′, wherein R and R′ areindependently hydrogen or a C₁-C₁₀ alkyl group), a hydrazone group(—CR═NHNR′R″, wherein R, R′ and R″ are independently hydrogen or aC₁-C₁₀ alkyl group), a carboxyl group (—CO₂H) or a salt thereof, asulfonyl group, a sulfamoyl group, a sulfonic acid group (—SO₃H) or asalt thereof, a phosphoric acid (—P(═O)(OH)₂) or a salt thereof, or aC₁-C₁₀ alkyl group, a C₂-C₁₀ alkenyl group, a C₂-C₁₀ alkynyl group, or aC₁-C₁₀ heteroalkyl group.

An amount of the piperazine derivative may be from about 0.005 percentby weight (“wt %”) or greater to less than about 10 wt % based on atotal weight of the electrolyte. For example, the amount of thepiperazine derivative may be from about 0.01 wt % to about 7 wt %, insome embodiments, from about 0.05 wt % to about 5 wt %, and in someother embodiments, from about 0.01 wt % to about 1 wt %, based on thetotal weight of the electrolyte. When the amount of the piperazinederivative is within these ranges, the piperazine derivative may bedissolved in the electrolyte while suppressing a side reaction of theelectrolyte, thus forming a thin film on a cathode surface to facilitateconducting of lithium ions between the cathode and the electrolyte.

The electrolyte of a lithium secondary battery serves as a path forlithium ions. Accordingly, if the electrolyte is oxidized or reducedthrough reaction with an electrode active material during charging anddischarging the battery, migration of lithium ions through theelectrolyte may be impaired, thus deteriorating charging and dischargingperformances of the lithium secondary battery.

An oxidation potential of the piperazine derivative may be lower than anoxidation potential of a non-aqueous organic solvent of the electrolyte,for example, by about 2 Volts (“V”) to about 4 V. Accordingly, when alithium secondary battery using an electrolyte including the piperazinederivative is operated, the piperazine derivative may be oxidized and/ordecomposed at a higher rate than that of the non-aqueous organicsolvent, thus resulting in a stable thin film on a surface of anelectrode, for example, a cathode. Although the film formation mechanismhas not been found yet, ring opening or polymerization of the additivevia oxidation may form a thin film. The thin film formed on the surfaceof the cathode blocks a cathode active material from directly contactingthe electrolyte, thereby preventing the electrolyte from oxidizing onthe surface of the cathode, and the charging and discharging performancefrom deteriorating. The thin film on the surface of the cathode mayserve as a migration path for lithium ions, and thus, a lithiumsecondary battery including the thin film may have improved lifetimecharacteristics and improved high-rate characteristics.

The non-aqueous organic solvent, which is in the electrolyte of alithium secondary battery according to the above-described embodiments,may serve as a migration medium of ions involved in electrochemicalreactions of the battery. Any suitable non-aqueous organic solvent thatis commonly used in the art may be used. For example, the non-aqueousorganic solvent may be a carbonate compound, an ester compound, an ethercompound, a ketone compound, an alcohol compound, an aprotic bipolarsolvent, or a combination thereof.

The carbonate compound may be an open chain carbonate compound, a cycliccarbonate compound, a fluoro carbonate derivative thereof, or acombination thereof.

Non-limiting examples of the chain carbonate compound are diethylcarbonate (“DEC”), dimethyl carbonate, (“DMC”), dipropyl carbonate(“DPC”), methylpropyl carbonate (“MPC”), ethylpropylcarbonate (“EPC”),methylethyl carbonate (“MEC”), and a combination thereof. Non-limitingexamples of the cyclic carbonate compound are ethylene carbonate (“EC”),propylenecarbonate (“PC”), butylene carbonate (“BC”), fluoroethylenecarbonate (“FEC”), vinylethylene carbonate (“VEC”), and a combinationthereof.

Non-limiting examples of the fluorocarbonate compound are fluoroethylenecarbonate (“FEC”), 4,5-difluoroethylene carbonate, 4,4-difluoroethylenecarbonate, 4,4,5-trifluoroethylene carbonate,4,4,5,5-tetrafluoroethylene carbonate, 4-fluoro-5-methylethylenecarbonate, 4-fluoro-4-methylethylene carbonate,4,5-difluoro-4-methylethylene carbonate,4,4,5-trifluoro-5-methylethylene carbonate, trifluoromethylethylenecarbonate, and a combination thereof.

The carbonate compound may include a combination of cyclic carbonate andchain carbonate, in consideration of dielectric constant and viscosityof the electrolyte. For example, when an amount of a cyclic carbonatecompound is at least 10% by volume based on a total volume of thenon-aqueous organic solvent, cycle characteristics of a lithiumsecondary battery may be markedly improved.

The carbonate compound may be a mixture of such chain carbonate and/orcyclic carbonate compounds as described above with a fluorocarbonatecompound. The fluorocarbonate compound may increase solubility of alithium salt to improve ionic conductivity of the electrolyte, and mayfacilitate formation of the thin film on the anode. In some embodiments,the fluorocarbonate compound may be fluoroethylene carbonate (“FEC”). Anamount of the fluorocarbonate compound may be from about 1 to about 30percent by volume (“volume %”) based on a total volume of thenon-aqueous organic solvent. When the amount of the fluorocarbonatecompound is within this range, the electrolyte may have an appropriateviscosity to provide desired effects thereof.

Non-limiting examples of the ester compound are methyl acetate, ethylacetate, n-propyl acetate, dimethyl acetate, methyl propionate (“MP”),ethyl propionate, y-butyrolactone, decanolide, valerolactone,mevalonolactone, caprolactone, and methyl formate. Non-limiting examplesof the ether compound are dibutyl ether, tetraglyme, diglyme,1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane,2-methyltetrahydrofuran, and tetrahydrofuran. An example of the ketonecompound is cyclohexanone. Non-limiting examples of the alcohol compoundare ethyl alcohol and isopropyl alcohol.

Examples of the aprotic solvent are nitriles (such as R—CN, wherein R isa C2-C20 linear, branched, or cyclic hydrocarbon-based moiety that mayinclude a double-bond, an aromatic ring or an ether bond), amides (suchas formamide and dimethylformamide), dioxolanes (such as 1,2-dioxolaneand 1,3-dioxolane), methylsulfoxide, sulfolanes (such as sulfolane andmethylsulfolane), 1,3-dimethyl-2-imidazolidinone,N-methyl-2-pyrrolidinone, nitromethane, trimethyl phosphate, triethylphosphate, trioctyl phosphate, and triester phosphate.

The non-aqueous organic solvent may be used alone or in a combination ofat least two solvents. In the latter case, a mixing ratio of the atleast two non-aqueous organic solvents may be appropriately adjusteddepending on a desired performance of the battery.

The non-aqueous organic solvent may further include an aromatichydrocarbon organic solvent in the carbonate solvent. The carbonatesolvent and the aromatic hydrocarbon organic solvent may be mixed, forexample, in a volume ratio of about 1:1 to about 30:1.

An example of the aromatic hydrocarbon organic solvent is an aromatichydrocarbon-based compound represented by formula below:

In the formula above, R_(a) to R_(f) may be each independently ahydrogen atom, a halogen atom, a C₁-C₁₀ alkyl group, a haloalkyl group,or a combination thereof.

Examples of the aromatic hydrocarbon organic solvent are benzene,fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene,1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene,chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene,1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene,iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene,1,2,3-triiodobenzene, 1,2,4-triiodobenzene, 2-fluorotoluene,3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene,2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-difluorotoluene,3,4-difluorotoluene, 3,5-difluorotoluene, 2,3,4-trifluorotoluene,2,3,5-trifluorotoluene, 2,3,6-trifluorotoluene, 3,4,5-trifluorotoluene,2,4,5-trifluorotoluene, 2,4,6-trifluorotoluene, 2-chlorotoluene,3-chlorotoluene, 4-chlorotoluene, 2,3-dichlorotoluene,2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,6-dichlorotoluene,2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, 2,3,6-trichlorotoluene,3,4,5-trichlorotoluene, 2,4,5-trichlorotoluene, 2,4,6-trichlorotoluene,2-iodotoluene, 3-iodotoluene, 4-iodotoluene, 2,3-diiodotoluene,2,4-diiodotoluene, 2,5-diiodotoluene, 2,6-diiodotoluene,3,4-diiodotoluene, 3,5-diiodotoluene, 2,3,4-triiodotoluene,2,3,5-triiodotoluene, 2,3,6-triiodotoluene, 3,4,5-triiodotoluene,2,4,5-triiodotoluene, 2,4,6-triiodotoluene, o-xylene, m-xylene,p-xylene, and combinations thereof.

The lithium salt, which is in the electrolyte of a lithium secondarybattery according to the above embodiment, may be soluble in the organicsolvent, and serves as a lithium ion source in the lithium secondarybattery to enable routine operation of the lithium secondary battery.The lithium salt may be any suitable lithium salt that is commonly usedfor lithium batteries. Examples of the lithium salt for the non-aqueouselectrolyte are LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiSbF₆, LiCF₃SO₃,Li(CF₃SO₂)₃C, Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiClO₄, LiAlO₄, LiAlCl₄, LiAlF₄,LiBPh₄, LiB₁₀Cl₁₀, CH₃SO₃Li, C₄F₃SO₃Li, (CF₃SO₂)₂NLi,LiN(C_(x)F_(2x+1)SO₂)(C_(x)F_(2y+1)SO₂) (wherein x and y are naturalnumbers), CF₃CO₂Li, LiCl, LiBr, LiI, LIBOB (lithium bisoxalato borate),lower aliphatic carboxylic acid lithium, lithium terphenylborate,lithium imide, and a combination thereof. These lithium salts may beused as a supporting electrolytic salt.

A concentration of the lithium salt may be within a range known to oneof ordinary skill in the art. The concentration of the lithium salt isnot specifically limited, and in some embodiments, may be in a range ofabout 0.1 molar (“M”) to about 2.0 M in the electrolyte to improvepractical performance of a lithium battery. When the concentration ofthe lithium salt is within this range, the electrolyte may haveappropriate conductivity and appropriate viscosity for improvedperformance, and may improve mobility of lithium ions.

In some embodiments, the electrolyte for a lithium battery may furtherinclude an additive to facilitate the formation of a stable solidelectrolyte interphase (“SEI”) or a thin film on a surface of anelectrode to provide improved cycle characteristics.

Non-limiting examples of the additive are tris(trimethylsilyl)phosphate(“TMSPa”), lithium difluoro oxalate borate (“LiFOB”), vinylene carbonate(“VC”), propane sulfone (“PS”), succinonitrile (“SN”), LiBF₄, a silanecompound having a functional group able to form a siloxane bond (forexample, acryl, amino, epoxy, methoxy, ethoxy, or vinyl), and a silazanecompound such as hexamethyldisilazane. These additives may be used aloneor in a combination of at least two thereof.

An amount of the additive may be from about 0.01 wt % to about 10 wt %based on a total weight of the non-aqueous organic solvent. For example,the amount of the additive may be from 0.05 wt % to about 10 wt %, insome embodiments, from about 0.1 wt % to about 5 wt %, and in some otherembodiments, from about 0.5 wt % to about 4 wt %, based on the totalweight of the non-aqueous organic solvent. However, the amount of theadditive is not particularly limited unless the additive significantlyhinders improvement in capacity retention rate of a lithium batteryincluding the electrolyte.

Hereinafter, embodiments of a lithium secondary battery including any ofthe electrolytes according to the above-described embodiments will bedescribed in detail.

According to an embodiment of the present disclosure, a lithium batteryincludes a cathode,

-   an anode and-   an electrolyte disposed between the cathode and the anode.

The lithium battery may be manufactured using a method known in the art.As described in the above embodiments, the electrolyte of the lithiumbattery may include a lithium salt, a non-aqueous organic solvent, and apiperazine derivative having an oxidation potential lower than anoxidation potential of the non-aqueous organic solvent by about 2 V toabout 4 V, wherein the piperazine derivative may include a compoundrepresented by Formula 1 above. The piperazine derivative of Formula 1above, the non-aqueous organic solvent, and the lithium salt are thesame as those described in the previous embodiments.

A thin film may be disposed between the cathode and the electrolyte. Thethin film is not a film formed via an additional process, such ascoating. The thin film may be a film derived from at least a part of theadditive in the electrolyte. The piperazine derivative of Formula 1above has both nitrogen moiety having an electron-donating non-covalentelectron pair and a polar functional group, and thus may be oxidizedbefore the oxidation of the electrolyte for forming a thin film on acathode surface.

In the electrolyte of the lithium secondary battery, since thepiperazine derivative of Formula 1 above forms the thin film on thesurface of the cathode, the amount of the piperazine compound may bereduced after operation of the lithium secondary battery.

For example, the amount of the piperazine compound in the electrolyteafter operation of the lithium secondary battery may be smaller thanthat before the operation of the lithium secondary battery.

According to the above-embodiments of the present disclosure, thelithium secondary battery may have a thin film formed on the surface ofthe cathode due to oxidation of at least a part of the additive in theelectrolyte during initial charging of the lithium secondary battery.Thus, the lithium secondary battery may have improved capacity retentioncharacteristics, lifetime characteristics and high-rate characteristicseven when charged at a high operating voltage of about 4.0 V to about5.5 V, for example, a voltage about 4.3 V to about 5.5 V.

When using the electrolyte including the piperazine derivative, thelithium secondary battery may further include a thin film on a surfaceof the cathode, the thin film having a thickness of, for example, about0.05 nanometers (“nm”) to about 100 nm. For example, the thin film mayhave a thickness of about 0.1 nm to about 80 nm, and in someembodiments, about 0.5 nm to about 50 nm. The thin film on the cathodesurface may effectively prevent oxidation of the electrolyte on thecathode surface so that the conduction of lithium ions is not impeded.

FIG. 1 is a schematic cross-sectional view illustrating a thin filmformed on a surface of a cathode of a lithium secondary battery,according to an exemplary embodiment. Referring to FIG. 1, a durablethin film 26 is formed on surfaces of cathode active material 22 appliedon a cathode current collector 20. As illustrated in FIG. 1, lithiumions 24 may effectively migrate from the cathode to the electrolyte 28.

FIG. 2 is an exploded perspective view of a lithium secondary battery100 according to an embodiment. Although the lithium secondary battery100 illustrated in FIG. 2 is cylindrical, embodiments of the presentdisclosure are not limited thereto, and lithium secondary batteriesaccording to embodiments may be of a rectangular type or a pouch type.

Lithium secondary batteries may be classified as lithium ion batteries,lithium ion polymer batteries, or lithium polymer batteries, accordingto the type of separator and/or electrolyte included therein. Inaddition, lithium batteries may be classified as cylindrical type,rectangular type, coin type, or pouch type, according to the shapethereof. Lithium batteries may also be classified as either bulk type orthin film type, according to the size thereof. Lithium secondarybatteries according to embodiments may have any appropriate shape. Thestructure of a lithium secondary battery and a method of manufacturingthe same are known in the art, so a detailed description thereof willnot be recited here.

Referring to FIG. 2, the lithium secondary battery 100, which iscylindrical, includes an anode 112, a cathode 114, a separator 113disposed between the anode 112 and the cathode 114, and an electrolyte(not shown) impregnated into the anode 112, the cathode 114 and theseparator 113, a battery case 120, and a sealing member 140 sealing thebattery case 120. The lithium secondary battery 100 is manufactured bysequentially stacking the anode 112, the cathode 114, and the separator113 upon one another to form a stack, rolling the stack in a spiralform, and accommodating the rolled up stack in the battery case 120.

The cathode 114 includes a cathode current collector, and a cathodeactive material layer disposed on the cathode current collector.

The cathode current collector may have a thickness of about 3micrometers (“μm”) to about 500 μm. The cathode current collector is notparticularly limited, and may be formed of any material so long as ithas a suitable conductivity without causing chemical changes in thefabricated battery. Examples of the cathode current collector includecopper, stainless steel, aluminum, nickel, titanium, sintered carbon,copper or stainless steel that is surface-treated with carbon, nickel,titanium or silver, and aluminum-cadmium alloys. In addition, thecathode current collector may be processed to have fine irregularitieson surfaces thereof so as to enhance adhesive strength of the cathodecurrent collector to the cathode active material, and may be used in anyof various forms including films, sheets, foils, nets, porousstructures, foams, and non-woven fabrics.

The cathode active material layer includes a cathode active material, abinder, and optionally a conducting agent.

Any lithium-containing metal oxide that is commonly used in the art maybe used as the cathode active material. The common cathode activematerial may be at least one of a composite oxide of lithium with ametal selected from Co, Mn, Ni, and a combination thereof. For example,the common cathode active material may be at least one of compoundsrepresented by the following formula: Li_(a)A_(1−b)B_(b)D₂ (wherein0.90≦a≦1, and 0≦b≦0.5); Li_(a)E_(1−b)B_(b)I_(2−c)D_(c) (wherein0.90≦a≦1, 0≦b≦0.5, and 0≦c≦0.05); LiE_(2−b)B_(b)O_(4−c)D_(c) (wherein0≦b≦0.5, and 0≦c≦0.05); Li_(a)Ni_(1−b−c)Co_(b)B_(c)D_(α) (wherein0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<α≦2);Li_(a)Ni_(1−b−c)Co_(b)B_(c)O_(2−α)F_(α) (wherein 0.90≦a≦1, 0b≦0.5,0≦c≦0.05, and 0<α<2); Li_(a)Ni_(1−b−c)Co_(b)B_(c)O_(2−α)F₂ (wherein0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2);Li_(a)Ni_(1−b−c)Mn_(b)B_(c)D_(α) (wherein 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05,and 0<α≦2); Li_(a)Ni_(1−b−c)Mn_(b)B_(c)O_(2−α)F₂ (wherein 0.90≦a≦1,0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li_(a)Ni_(1−b−c)Mn_(b)B_(c)O_(2−α)F₂(wherein 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2);Li_(a)Ni_(b)E_(c)G_(d)O₂ (wherein 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, and0.001≦d≦0.1); Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂ (wherein 0.90≦a≦1, 0≦b≦0.9,0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1); Li_(a)NiG_(b)O₂ (wherein 0.90≦a≦1,and 0.001≦b≦0.1); Li_(a)CoG_(b)O₂ (wherein 0.90≦a≦1, and 0.001≦b≦0.1);Li_(a)MnG_(b)O₂ (wherein 0.90≦a≦1, and 0.001≦b≦0.1); Li_(a)Mn₂G_(b)O₄(wherein 0.90≦a≦1, and 0.001≦b≦0.1); QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₅;LiIO₂; LiNiVO₄; Li_((3−f))J₂(PO₄)₃ (wherein 0≦f≦2); Li_((3−f))Fe₂(PO₄)₃(wherein 0≦f≦2); LiFePO₄.

In the formulae above, A is selected from nickel (Ni), cobalt (Co),manganese (Mn), and combinations thereof; B is selected from aluminum(Al), nickel (Ni), cobalt (Co), manganese (Mn), chromium (Cr), iron(Fe), magnesium (Mg), strontium (Sr), vanadium (V), a rare earthelement, and combinations thereof; D is selected from oxygen (O),fluorine (F), sulfur (S), phosphorus (P), and combinations thereof; E isselected from cobalt (Co), manganese (Mn), and combinations thereof; Fis selected from fluorine (F), sulfur (S), phosphorus (P), andcombinations thereof; G is selected from aluminum (Al), chromium (Cr),manganese (Mn), iron (Fe), magnesium (Mg), lanthanum (La), cerium (Ce),strontium (Sr), vanadium (V), and combinations thereof; Q is selectedfrom titanium (Ti), molybdenum (Mo), manganese (Mn), and combinationsthereof; I is selected from chromium (Cr), vanadium (V), iron (Fe),scandium (Sc), yttrium (Y), and combinations thereof; and J is selectedfrom vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), nickel(Ni), copper (Cu), and combinations thereof.

In some embodiments, the cathode active material may be LiCoO₂,LiMn_(x)O_(2x) (wherein x=1 or 2), LiNi_(1−x)Mn_(x)O_(2x) (wherein0<x<1), LiNi_(1−x−y)Co_(x)Mn_(y)O₂ (wherein 0≦x≦0.5 and 0≦y≦0.5), orFePO₄.

In some other embodiments, the cathode active material may include atleast one of LiCoO₂, LiNi_(1−x)Co_(x)O₂ (wherein 0≦x<1), Li_(1−x)M_(x)O₂(wherein M is at least one of Mn and Fe, and 0.03<x<0.1),Li[Ni_(x)Co_(1−2x)Mn_(x)]O₂ (wherein 0<x<0.5), Li[Ni_(x)Mn_(x)]O₂(wherein 0<x≦0.5), Li_(1+x)(Ni,Co,Mn)_(1−y)O_(z) (wherein 0<x≦1, 0≦y<1,and 2≦z≦4), LiM₂O₄ (wherein M is at least one of Ti, V, and Mn),LiM_(x)Mn_(2−x)O₄ (wherein M is a transition metal), LiFePO₄, LiMPO₄(wherein M is at least one of Mn, Co, and Ni), V₂O₅, V₂O₃, VO₂(B),V₆O₁₃, V₄O₉, V₃O₇, Ag₂V₄O₁₁, AgVO₃, LiV₃O₅, δMn_(y)V₂O₅, δ-NH₄V₄O₁₀,Mn_(0.8)V₇O₁₆, LiV₃O₈, Cu_(x)V₂O₅, Cr_(x)V₆O₁₃, M₂(XO₄)₃ (wherein M is atransition metal, and X is at least one of S, P, As, Mo, and W), andLi₃M₂(PO₄)₃ (wherein M is at least one of Fe, V, and Ti).

For example, the cathode active material may includeLi_(1+x)M_(1−x)O₂(wherein M is at least one of Ni, Co, and Mn, and0.05≦x≦0.2) or LiNi_(0.5)Mn_(1.5)O₄. These cathode active materials maybe used in implementing high-voltage lithium secondary batteries.

The compounds listed above as cathode active materials may have asurface coating layer (hereinafter, “coating layer”). Alternatively, amixture of a compound without a coating layer and a compound having acoating layer, the compounds being selected from the compounds listedabove, may be used. The coating layer may include at least one compoundof a coating element selected from oxide, hydroxide, oxyhydroxide,oxycarbonate, and hydroxycarbonate of the coating element. The compoundsfor the coating layer may be amorphous or crystalline. The coatingelement for the coating layer may be magnesium (Mg), aluminum (Al),cobalt (Co), potassium (K), sodium (Na), calcium (Ca), silicon (Si),titanium (Ti), vanadium (V), tin (Sn), germanium (Ge), gallium (Ga),boron (B), arsenic (As), zirconium (Zr), or mixtures thereof. Thecoating layer may be formed using any method that does not adverselyaffect the physical properties of the cathode active material when acompound of the coating element is used. For example, the coating layermay be formed using a spray coating method, a dipping method, or anyother method known to one of ordinary skill in the art. Thus, a detaileddescription thereof will be omitted herein.

The binder strongly binds positive cathode active material particlestogether and to a current collector. Examples of the binder are, but notlimited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropylcellulose, diacetyl cellulose, polyvinyl chloride, carboxylatedpolyvinyl chloride, polyvinyl fluoride, a polymer including ethyleneoxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene,polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadienerubber (“SBR”), acrylated SBR, epoxy resin, and nylon.

The conducting agent is used to provide conductivity to electrodes. Anyelectron conducting material that does not induce chemical change inbatteries may be used. Examples of the conducting agent include naturalgraphite, artificial graphite, carbon black, acetylene black, ketjenblack, carbon fibers, and metallic materials, including copper, nickel,aluminum, and silver, in powder or fiber form. The conducting agent mayinclude a single conductive material, such as a polyphenylenederivative, or a combination of at least two conductive materials.

The amounts of the cathode active material, the binder, and theconducting agent may be equivalent to those commonly used in lithiumbatteries. For example, a weight ratio of the cathode active material toa mixture of the conducting agent and the binder may be from about 98:2to about 92:8, and in some embodiments from about 95:5 to about 90:10. Amixing ratio of the conducting agent to the binder may be, but notlimited, from about 1:1.5 to about 1:3.

The cathode active material may have, for example, an operating voltagerange of about 4.0 V to about 5.5 V.

The anode 112 includes an anode current collector and a cathode activematerial layer disposed on the anode current collector.

The anode current collector may have, for example, a thickness of about3 μm to about 500 μm. The anode current collector is not particularlylimited, and may be formed of any material so long as it has a suitableconductivity without causing chemical changes in the fabricated battery.Examples of the anode current collector are copper, stainless steel,aluminum, nickel, titanium, sintered carbon, copper or stainless steelthat is surface-treated with carbon, nickel, titanium or silver, andaluminum-cadmium alloys. In addition, the anode current collector may beprocessed to have fine irregularities on surfaces thereof so as toenhance adhesive strength of the anode current collector to the anodeactive material, and may be used in any of various forms includingfilms, sheets, foils, nets, porous structures, foams, and non-wovenfabrics.

The anode active layer includes an anode active material, a binder, andoptionally a conducting agent.

The anode active material is not particularly limited, and may beselected from any anode active materials used in the art. Non-limitingexamples of the anode active material are lithium metal, a lithium metalalloy, a transition metal oxide, a material that allows doping orundoping of lithium, and a material that allows reversible intercalationand deintercalation of lithium ions, which may be used as a mixture orin combination of at least two thereof.

The lithium metal alloy may be an alloy of lithium with a metal selectedfrom sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium(Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr),silicon (Si), antimony (Sb), lead (Pb), indium (In), zinc (Zn), barium(Ba), radium (Ra), germanum (Ge), aluminum (Al), and tin (Sn).

Non-limiting examples of the transition metal oxide are tungsten oxide,molybdenum oxide, titanium oxide, lithium titanium oxide, vanadiumoxide, and lithium vanadium oxide.

Examples of the material that allows doping or undoping of lithiumtherein are Si, Sn, Al, Ge, Pb, Bi, Sb, and a Si—Y alloy (where Y is analkali metal, a alkali earth metal, a Group 11 element, a Group 12element, a Group 13 element, a Group 14 element, a Group 15 element, aGroup 16 element, a transition metal, a rare earth element, and acombination thereof, except for Sn. For example, Y may be magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), scandium(Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf),rutherfordium (Rf), vanadium (V), niobium (Nb), tantalum (Ta), dubnium(Db), chromium (Cr), molybdenum (Mo), tungsten (W), seaborgium (Sg),technetium (Tc), rhenium (Re), bohrium (Bh), iron (Fe), lead (Pb),ruthenium (Ru), osmium (Os), hassium (Hs), rhodium (Rh), iridium (Ir),palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc(Zn), cadmium (Cd), boron (B), aluminum (Al), gallium (Ga), tin (Sn),indium (In), titanium (Ti), germanium (Ge), phosphorus (P), arsenic(As), antimony (Sb), bismuth (Bi), sulfur (S), selenium (Se), tellurium(Te), polonium (Po), or combinations thereof.

The material that allows reversible intercalation and deintercalation oflithium ions may be any carbonaceous anode active material that iscommonly used in a lithium battery. Examples of such carbonaceousmaterials are crystalline carbon, amorphous carbon, or mixtures thereof.Non-limiting examples of the crystalline carbon are natural graphite,artificial graphite, expanded graphite, graphene, fullerene soot, carbonnanotubes, and carbon fiber. Non-limiting examples of the amorphouscarbon are soft carbon (carbon sintered at low temperatures), hardcarbon, meso-phase pitch carbides, and sintered corks. The carbonaceousanode active material may be in, for example, spherical, planar,fibrous, tubular, or powder form.

The binder strongly binds anode active material particles together andto the anode current collector. Non-limiting examples of the binder arepolyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose,diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride,polyvinyl fluoride, a polymer including ethylene oxide,polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene,polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadienerubber (“SBR”), acrylated SBR, epoxy resin, and nylon.

The conducting agent is used to provide conductivity to the anode. Anyelectron conducting material that does not induce chemical change inbatteries may be used. Examples of the conducting agent are carbonaceousmaterials, such as natural graphite, artificial graphite, carbon black,acetylene black, ketjen black, carbon fibers, and the like; metal-basedmaterials, such as copper (Cu), nickel (Ni), aluminum (Al), silver (Ag),and the like, in powder or fiber form; and conductive materials,including conductive polymers, such as a polyphenylene derivative, andmixtures thereof.

The amounts of the anode active material, the binder, and the conductingagent may be equivalent to those commonly used in lithium batteries. Forexample, a weight ratio of the anode active material to a mixture of theconducting agent and the binder may be from about 98:2 to about 92:8. Amixing ratio of the conducting agent to the binder may be, but notlimited to, from about 1:1.5 to about 1:3.

The anode 112 and the cathode 114 may be each manufactured by mixing anactive material, a conducting agent, and a binder in a solvent toprepare an active material composition, and coating the active materialcomposition on a current collector. Any method of manufacturing suchelectrodes which is known to one of ordinary skill in the art may beused. Thus, a detailed description thereof will not be provided herein.Non-limiting examples of the solvent are N-methylpyrrolidone (“NMP”),acetone, and water.

A separator may be disposed between the cathode and the anode, accordingto the type of the lithium secondary battery. The separator may be anyseparator that is commonly used for lithium batteries. In particular,the separator may have low resistance to migration of ions in anelectrolyte and have high electrolyte-retaining ability. Examples of theseparator are glass fiber, polyester, Teflon, polyethylene,polypropylene, polyvinylidene fluoride (“PVDF”), polytetrafluoroethylene(“PTFE”), and a combination thereof, each of which may be a nonwovenfabric or a woven fabric. The separator may be a single layer or amulti-layer. Examples of the separator are a polyethylene/polypropylenedouble-layer separator, polyethylene/polypropylene/polyethylenetriple-layer separator, and a polypropylene/polyethylene/polypropylenetriple-layer separator. The separator may have a pore diameter of about0.01 to about 10 μm and a thickness of about 3 to about 100 μm.

As described in the above embodiments, the electrolyte of the lithiumsecondary battery may include a lithium salt, a non-aqueous organicsolvent, and a piperazine derivative of Formula 1 above with a polarsubstituent as an additive. The electrolyte may be injected between thecathode 114 and the anode 112 with the separator 113 therebetween.

One or more embodiments will now be described in detail with referenceto the following examples. However, these examples are not intended tolimit the scope of the one or more embodiments.

EXAMPLES Example 1

0.1 wt % of 1-(2-aminoethyl)piperazine (“AEP”) represented by Formula 3below as an additive was added into a mixed organic solvent of 30 volume% of ethylene carbonate, 50 volume % of diethyl carbonate, and 20 volume% of ethylmethyl carbonate, and 1.3 M LiPF₆ as a lithium salt was addedthereto, thereby preparing an electrolyte for a lithium secondarybattery (Electrolyte A).

Li_(1+x)(Ni,Co,Mn)_(1−x)O₂ (wherein 0.05≦x≦0.25) powder as a cathodeactive material, 5 percent by weight (“wt %”) of polyvinylidene fluoride(“PVdF”) binder dissolved in N-methylpyrrolidone (“NMP”), and aconducting agent (Denka black) were mixed in a weight ratio of 90:5:5 toprepare a cathode forming slurry. The cathode forming slurry was coatedon an aluminum foil having a thickness of 15 μm. The aluminum foilcoated with the cathode forming slurry was dried in a 90° C. oven forabout 2 hours (first drying), and then in a 120° C. vacuum oven forabout 2 hours (second drying) until the NMP was completely evaporated,followed by rolling and punching to obtain a cathode having a diameterof about 1.5 centimeters (“cm”) and a thickness of about 50˜60 μm foruse in a coin cell. The cathode had a capacity of about 1.9milliAmpere×hour per square centimeter (“mA×h/cm²”).

The cathode, a graphite anode (ICG10H, available from Mitsubishi), apolyethylene separator (Celgard 3501, available from Celgard), and theelectrolyte A prepared as described above were used to manufacture a2032 standard coin cell.

Example 2

A lithium secondary battery was manufactured in the same manner as inExample 1, except that 0.1 wt % of 1,4-bis(2-hydroxyethyl)piperazine(“BHEP”) represented by Formula 4 below, instead of AEP of Formula 3 wasused as the additive.

Example 3

A lithium secondary battery was manufactured in the same manner as inExample 1, except that 0.1 wt % of 1-(2-hydroxyphenyl)piperazine (“HPP”)represented by Formula 5 below, instead of AEP of Formula 3, was used asthe additive.

Example 4

A lithium secondary battery was manufactured in the same manner as inExample 1, except that 0.1 wt % of 3-piperazino propionitrile (“PCN”)represented by Formula 6 below, instead of AEP of Formula 3, was used asthe additive.

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as inExample 1, except that a standard electrolyte (“STD”) excluding AEP ofFormula 3 was used.

Comparative Example 2

A lithium secondary battery was manufactured in the same manner as inExample 1, except that 0.1 wt % of piperazine (“PPR”) represented byFormula 7 below, instead of AEP of Formula 3, was used as the additive.

Comparative Example 3

A lithium secondary battery was manufactured in the same manner as inExample 1, except that 0.1 wt % of 1-(2-hydroxyethyl)piperazine (“HEP”)represented by Formula 8 below, instead of AEP of Formula 3, was used asthe additive.

Comparative Example 4

A lithium secondary battery was manufactured in the same manner as inExample 1, except that 0.1 wt % of 1-(2-pyrimidyl)piperazine (“PMP”)represented by Formula 9, instead of AEP of Formula 3, was used as theadditive.

Evaluation Example 1 Measurement of Oxidation Potential of Additive

Oxidation potentials of AEP, BHEP, HPP, PCN, PPR, HEP, and PMP used aselectrolyte additives in Examples 1-4 and Comparative Examples 2-4,respectively, were calculated using density functional theory (DFT;B3LYP/6-311+G(d,p))-based ab-initio calculation (Gaussian 03). Theresults are shown in Table 1 below. In calculating the oxidationpotentials, oxidation reaction as illustrated below is was considered.M(solution)→M ⁺(solution)+e ⁻(gas)

In this oxidation reaction, M and e indicate molecules and electrons ofthe additive, respectively.

A polarized continuum model (“PCM”) was used in consideration of effectsof neighboring electrolyte environment around additive molecules on theoxidation potential of the additive.

TABLE 1 E_(ox)/ E_(red) (V vs. Example Compound Structure Li) Example 11-(2- aminoethyl) piperazine

3.58/ −1.22 Example 2 1,4-bis(2- hydroxyethyl) piperazine

3.49/ −0.87 Example 3 1-(2- hydroxy- phenyl) piperazine

3.49/ −0.49 Example 4 3-piperazino propionitrile

3.48/ −0.01 Com- parative Example 2 piperazine

3.56/ −1.28 Com- parative Example 3 1-(2- hydroxy- ethyl) piperazine

3.39/ −0.89 Com- parative Example 4 1-(2- pyrimidyl) piperazine

3.81/ 0.42 Non- aqueous organic solvent EMC

6.55 Non- aqueous organic solvent DEC

6.6  Non- aqueous organic solvent EC

6.7 

Referring to Table 1 above, the piperazine derivatives used in Examples1-4 were found to have an oxidation potential lower by about 3 V orgreater than a common carbonate-based non-aqueous organic solvent, whichis known to have an oxidation potential of from about 6.5 V to about 6.7V. This indicates that a lithium secondary battery using an electrolytecontaining such a piperazine derivative as used in Examples 1-4 islikely to be decomposed earlier than the non-aqueous organic solvent ofthe electrolyte, and effectively forms a thin film on a surface of thecathode.

Evaluation Example 2 Evaluation of Lifetime Characteristics

Formation Charge and Discharge

Formation charging/discharging was performed twice on the lithiumsecondary batteries of Examples 1-4 and Comparative Examples 1-4 at roomtemperature.

In a first formation process constant-current charging was performed oneach battery at 0.1 Coulomb (“C”) to a voltage of 4.65 V, followed byconstant-voltage charging to a 0.05 C current. Next, constant-currentdischarging was performed at 0.1 C to a voltage of 2.5 V. A secondformation process was performed in the same manner as in the firstformation process.

The term “1 C charging” refers to charging for 1 hour to reach thecapacity of a battery in milliAmpere hour (“mA×h”). Likewise, the term“1 C discharging” refers to discharging for 1 hour to fully dischargethe capacity of the battery in mA×h.

Standard Charge and Discharge

After the formation charging and discharging, each of the batteriesobtained in Examples 1-4 and Comparative Examples 1-4 was charged at 0.5C to a voltage of 4.55 V, and then discharged at 0.2 C to a voltage of2.5 V. These charging and discharging conditions were termed as“standard charging and discharging conditions”, and the dischargecapacity in these conditions was defined as a “standard capacity”. Themeasured standard capacities ranged from about 3.2 mA×h to about 3.5mA×h.

Capacity Retention Rate (%)

Charging was performed on each of the lithium secondary batteries ofExamples 1-4 and Comparative Examples 1-4 in a 25° C.constant-temperature chamber at 1 C to a voltage of 4.55 V, followed bydischarging at 1 C to a voltage of 2.8 V. Then, a discharge capacity(discharge capacity after the 1st cycle) was measured. While the cycleof 1 C charging and 1 C discharging was repeated in the 25° C. chamber,a discharge capacity after each cycle was measured. The charging anddischarging cycle was repeated 300 times in total. A capacity retentionrate was calculated using the discharge capacity from each of thecycles. The cycle retention was calculated using Equation 1 below.Capacity retention rate[%]=(n ^(th) cycle discharge capacity/1^(st)cycle discharge capacity)×100  Equation 1

FIG. 3 is a graph of discharge capacities of the lithium secondarybatteries of Examples 1 and 2, and Comparative Examples 1-4. FIG. 4 is agraph of average charge/discharge efficiencies of the lithium secondarybatteries of Examples 1 and 2 and Comparative Examples 1 and 2 whichwere calculated based on over 300 cycles of charging and discharging.

Referring to FIGS. 3 and 4, the lithium secondary batteries of Examples1 and 2 were found to have improved lifetime characteristics, ascompared with those of Comparative Examples 1 to 4.

Evaluation Example 3 Evaluation of High-Rate Characteristics

High-rate discharge characteristics (rate capacities) of the lithiumsecondary batteries of Examples 1-4 and Comparative Examples 1-4 wereevaluated after charging each cell at a constant current of 0.1 C and aconstant voltage of 1.0 V (0.01 C cut-off), a rest for about 10 minutes,and then discharging the batteries at a constant current of 0.2 C, 0.33C, 1 C, 2 C and 5 C, respectively, with a cut-off voltage of 2.5 V. Theresults are shown in FIG. 5.

Referring to FIG. 5, the lithium secondary batteries of Examples 1-4were found to have better high-rate characteristics, as compared withthe lithium secondary batteries of Comparative Examples 1-4.

After completion of the lifetime characteristics evaluation inEvaluation Example 1, the lithium secondary batteries of Examples 1 and2 and Comparative Example 1 and 2 were each disassembled in a glove boxto recover the cathode, which was then cleaned with dimethyl carbonateto remove the electrolyte and the lithium salt therefrom, and dried. Asurface material was taken from the cathode as a sample, which was thenanalyzed using an X-ray photoelectron spectroscope (“XPS”) (Sigma Probe,Thermo, UK). The results are shown in FIGS. 6A to 6C.

FIGS. 6A to 6C are X-ray photoelectron spectra illustrating the N 1 speak, Mn 2 p peak, and O 1 s peak, respectively, of the surface materialsampled from the surface of the cathode of each of the lithium secondarybatteries of Examples 1 and 2 and Comparative Examples 1 and 2.

Referring to FIGS. 6A to 6C, the surface materials sampled from thesurface of the cathode of the lithium secondary batteries of Examples 1and 2 were found to have larger N 1 s peaks in comparison to those ofComparative Examples 1 and 2, indicating that a thin film was formedfrom the piperazine derivative used as an additive in each of Examples 1and 2, while the surface materials sampled from the surface of thecathode of the lithium secondary batteries of Examples 1 and 2 werefound to have smaller Mn 2 p and O 1 s (layered oxide) peaks incomparison to those of Comparative Examples 1 and 2, indicating the thinfilms resulting from the additives may have improved passivation effectseven after the 300^(th) charge/discharge cycle.

Based on the results of FIGS. 6A to 6C, the lithium secondary battery ofExample 1 was found to have a thin film derived from Electrolyte A onthe surface of the cathode, wherein the thin film remains, notdecomposed, even after operation at high temperatures.

According to the one or more embodiments of the present disclosure, athin film may be formed on a surface of the cathode active material ofthe battery during initial charging and discharging, from an additive inthe electrolyte, and thus prevents direct contact of the electrolytewith the cathode active material. The thin film allows only lithium ionsto pass through, but not electrons, so that oxidation of the electrolytefrom losing electrons to the cathode in a high-temperature, high-voltagecondition may be prevented. The additive may be decomposed underhigh-temperature, high-voltage conditions to form the thin film, whichprevents decomposition of the electrolyte. The prevention of theelectrolyte loss under high-temperature and high-voltage conditions maysecure the lithium secondary battery to retain high capacity andefficiency, and thus to have longer lifetime.

The improvements in lifetime characteristics and high-temperaturestorage characteristics enable the lithium secondary batteries accordingto the above-described embodiments to normally operate in an extremeenvironment when used in electric vehicles or in power storages that areexposed to high-temperatures. According to the embodiments, theelectrolyte is also expected to be used in a lithium secondary batteryusing a cathode active material to which a far high voltage is applied,for example, a 5 V spinel, or a high-voltage phosphate cathode activematerial, taking an important part in improving the energy density ofbatteries for electric vehicles and power storages.

As described above, according to the one or more of the aboveembodiments, an electrolyte for a lithium secondary battery including apiperazine derivative of Formula 1 above may form a thin film on acathode surface of the lithium secondary battery, and thus may improvelithium ion conductivity and stability when the lithium secondarybattery is operated at a high-voltage. A lithium secondary batteryincluding the electrolyte may have improved lifetime characteristics andimproved high-rate characteristics due to suppressed oxidation anddecomposition of the electrolyte.

It should be understood that the exemplary embodiments described thereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While one or more embodiments of the present disclosure have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope of thepresent disclosure as defined by the following claims.

What is claimed is:
 1. A lithium secondary battery comprising: a cathodecomprising a cathode active material, an anode comprising an anodeactive material, and a non-aqueous liquid electrolyte comprising: alithium salt; a non-aqueous organic solvent; a piperazine derivativeadditive represented by Formula 1 having an oxidation potential lowerthan an oxidation potential of the non-aqueous organic solvent by about2 V to about 4 V:

wherein, in Formula 1, at least one of X and Y is selected from a C₁-C₆₀aminoalkyl group, a C₁-C₆₀ thioalkyl group, a C₁-C₆₀ hydroxyalkyl group,a C₁-C₆₀ alkylnitrile group, and a substituted C₆-C₆₀ aryl group, andthe unselected rest of X and Y is a hydrogen atom; R₁ to R₄ are eachindependently selected from a hydrogen atom, a deuterium atom, a halogenatom, a hydroxyl group, a cyano group, a nitro group, an azido group, anamino group, an amido group, an amidino group, a hydrazine group, ahydrazone group, a carboxyl group or a salt thereof, a sulfonic acidgroup or a salt thereof, a phosphoric acid group or a salt thereof, athiol group, —C(═O)—H, a substituted or unsubstituted C₁-C₆₀ alkylgroup, a substituted or unsubstituted C₁-C₆₀ alkoxy group, a substitutedor unsubstituted C₁-C₆₀ heteroalkyl group, a substituted orunsubstituted C₂-C₆₀ alkenyl group, a substituted or unsubstitutedC₂-C₆₀ alkynyl group, a substituted or unsubstituted C₃-C₁₀ cycloalkylgroup, a substituted or unsubstituted C₃-C₁₀ heterocycloalkyl group, asubstituted or unsubstituted C₂-C₁₀ cycloalkenyl group, a substituted orunsubstituted C₂-C₁₀ heterocycloalkenyl group, a substituted orunsubstituted C₆-C₆₀ aryl group, a substituted or unsubstituted C₆-C₆₀aryloxy group, a substituted or unsubstituted C₂-C₆₀ heteroaryl group,-(Q₁)_(r)-(Q₂)_(s), —N(Q₃)(Q₄)(Q₅), —P(═O)(Q₆)(Q₇), and—P(Q₈)(Q₉)(Q₁₀)(Q₁₁); wherein at least one of R₁₁ to R₁₄ and at leastone of R₂₁ to R₃₀ are optionally linked to each other to form asubstituted or unsubstituted, saturated or unsaturated ring; Q₁ is atleast one selected from —O—, —S—, —C(═O)—, a substituted orunsubstituted C₁-C₆₀ alkylene group, a substituted or unsubstitutedC₂-C₆₀ alkenylene group, a substituted or unsubstituted C₃-C₁₀cycloalkylene group, a substituted or unsubstituted C₃-C₁₀heterocycloalkylene group, a substituted or unsubstituted C₂-C₁₀cycloalkenylene group, a substituted or unsubstituted C₂-C₁₀heterocycloalkenylene group, a substituted or unsubstituted C₆-C₆₀arylene group, and a substituted or unsubstituted C₂-C₆₀ heteroarylenegroup; Q₂ to Q₁₁ are each independently selected from a deuterium atom,a halogen atom, a hydroxyl group, a cyano group, a nitro group, an azidogroup, an amino group, an amido group, an amid ino group, a hydrazinegroup, a hydrazone group, a carboxyl group or a salt thereof, a sulfonicacid group or a salt thereof, a phosphoric acid group or a salt thereof,a thiol group, a substituted or unsubstituted C₁-C₆₀ alkyl group, asubstituted or unsubstituted C₁-C₆₀ alkoxy group, a substituted orunsubstituted C₁-C₆₀ heteroalkyl group, a substituted or unsubstitutedC₂-C₆₀ alkenyl group, a substituted or unsubstituted C₂-C₆₀ alkynylgroup, a substituted or unsubstituted C₁-C₆₀ alkoxy group, a substitutedor unsubstituted C₃-C₁₀ cycloalkyl group, a substituted or unsubstitutedC₃-C₁₀ heterocycloalkyl group, a substituted or unsubstituted C₂-C₁₀cycloalkenyl group, a substituted or unsubstituted C₂-C₁₀heterocycloalkenyl group, a substituted or unsubstituted C₆-C₆₀ arylgroup, a substituted or unsubstituted C₆-C₆₀ aryloxy group, and asubstituted or unsubstituted C₂-C₆₀ heteroaryl group; and r and s areeach independently an integer from 1 to 5, wherein, when r is 2 orgreater, groups Q₁ are each identical to or different from each other,and when s is 2 or greater, groups Q₂ are each identical to or differentfrom each other, wherein the lithium secondary battery further comprisesa film disposed between the cathode and the electrolyte, wherein thefilm comprises at least a part of the additive.
 2. The lithium secondarybattery of claim 1, wherein R₁ to R₄ in Formula 1 are each independentlyselected from a hydrogen atom, a deuterium atom, a halogen atom, ahydroxyl group, a cyano group, a nitro group, an azido group, an aminogroup, an amido group, an amidino group, a hydrazine group, a hydrazonegroup, a carboxyl group or a salt thereof, a sulfonic acid group or asalt thereof, a phosphoric acid group or a salt thereof, a thiol group,—C(═O)—H, a methyl group, an ethyl group, an n-propyl group, anisopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group,a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentylgroup, a tert-pentyl group, an n-hexyl group, an isohexyl group, asec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptylgroup, a sec-heptyl group, a tert-heptyl group, an n-octyl group, anisooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group,an isononyl group, a sec-nonyl group, a tert-nonyl group, a n-decylgroup, an isodecyl group, a sec-decyl group, a tert-decyl group, and-(Q₁)_(r)-(Q₂)_(s), wherein Q₁ is selected from —O—, —S—, —C(═O)—, aC₁-C₁₀ alkylene group, a C₆-C₁₄ arylene group, and a C₂-C₁₄heteroarylene group; Q₂ is selected from a deuterium atom, a halogenatom, a hydroxyl group, a cyano group, a nitro group, an azido group, anamino group, an amido group, an amidino group, a hydrazine group, ahydrazone group, a carboxyl group or a salt thereof, a sulfonic acidgroup or a salt thereof, a phosphoric acid group or a salt thereof, athiol group, —C(═O)—H, a methyl group, an ethyl group, an n-propylgroup, an isopropyl group, an n-butyl group, an isobutyl group, a sec-abutyl group, a tert-butyl group, a n-pentyl group, an isopentyl group, asec-pentyl group, a tert-pentyl group, a n-hexyl group, an isohexylgroup, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, anisoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octylgroup, an isooctyl group, a sec-octyl group, a tert-octyl group, ann-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group,an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decylgroup, and a C₁-C₁₀ alkoxy group, and r and s are each independently aninteger from 1 to 5 wherein, when r is 2 or greater, groups Q₁ are eachidentical to or different from each other, and when s is 2 or greater,groups Q₂ are each identical to or different from each other.
 3. Thelithium secondary battery of claim 1, wherein R₁ to R₄ in Formula 1 areeach independently selected from a hydrogen atom, a deuterium atom, ahalogen atom, a hydroxyl group, a cyano group, a nitro group, an azidogroup, an amino group, an amido group, an amidino group, a hydrazinegroup, a hydrazone group, a carboxyl group or a salt thereof, a sulfonicacid group or a salt thereof, a phosphoric acid group or a salt thereof,a thiol group, —C(═O)—H, a methyl group, an ethyl group, an n-propylgroup, an isopropyl group, an n-butyl group, an isobutyl group, asec-butyl group, a tert-butyl group, an n-pentyl group, an isopentylgroup, a sec-pentyl group, a tert-pentyl group, an n-hexyl group, anisohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptylgroup, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, ann-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group,an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonylgroup, an n-decyl group, an isodecyl group, a sec-decyl group, atert-decyl group, and groups represented by Formulae 3A and 3B:

wherein, in Formulae 3A and 3B, Q₁a is a C₁-C₁₀ alkylene group; Q₂ isselected from a deuterium atom, a halogen atom, a hydroxyl group, acyano group, a nitro group, an azido group, an amino group, an amidogroup, an amidino group, a hydrazine group, a hydrazone group, acarboxyl group or a salt thereof, a sulfonic acid group or a saltthereof, a phosphoric acid group or a salt thereof, a thiol group,—C(═O)—H, a methyl group, an ethyl group, an n-propyl group, anisopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group,a tert-butyl group, an n-pentyl group, an isopentyl group, a sec-pentylgroup, a tert-pentyl group, an n-hexyl group, an isohexyl group, asec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptylgroup, a sec-heptyl group, a tert-heptyl group, an n-octyl group, anisooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group,an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decylgroup, an isodecyl group, a sec-decyl group, a tert-decyl group, and aC₁-C₁₀ alkoxy group; and s is an integer of 1, 2, or
 3. 4. The lithiumsecondary battery of claim 1, wherein the piperazine derivativecomprises a compound represented by Formula 2:

wherein, in Formula 2, at least one of X′ and Y′ is a substituentselected from a C₁-C₁₀ hydroxyalkyl group, a C₁-C₁₀ aminoalkyl group, aC₁-C₁₀ alkylnitrile group, and a substituted C₆-C₁₀ aryl group, and theunselected rest of X′ and Y′ is a hydrogen atom; R₁ to R₄ is eachindependently selected from a hydrogen atom, a deuterium atom, a halogenatom, a hydroxyl group, a cyano group, a nitro group, an azido group, anamino group, an amido group, an amidino group, a hydrazine group, ahydrazone group, a carboxyl group or a salt thereof, a sulfonic acidgroup or a salt thereof, a phosphoric acid group or a salt thereof, athiol group, —C(═O)—H, a methyl group, an ethyl group, an n-propylgroup, an isopropyl group, an n-butyl group, an isobutyl group, asec-butyl group, a tert-butyl group, an n-pentyl group, an isopentylgroup, a sec-pentyl group, a tert-pentyl group, an n-hexyl group, anisohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptylgroup, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, ann-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group,an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonylgroup, an n-decyl group, an isodecyl group, a sec-decyl group, atert-decyl group, and -(Q₁)_(r)-(Q₂)_(s), wherein Q₁ is selected from—O—, —S—, —C(═O)—, a C₁-C₁₀ alkylene group, a C₆-C₁₄ arylene group, anda C₂-C₁₄ heteroarylene group; Q₂ is selected from a deuterium atom, ahalogen atom, a hydroxyl group, a cyano group, a nitro group, an azidogroup, an amino group, an amido group, an amidino group, a hydrazinegroup, a hydrazone group, a carboxyl group or a salt thereof, a sulfonicacid group or a salt thereof, a phosphoric acid group or a salt thereof,a thiol group, —C(═O)—H, a methyl group, an ethyl group, an n-propylgroup, an isopropyl group, an n-butyl group, an isobutyl group, a sec-abutyl group, a tert-butyl group, a n-pentyl group, an isopentyl group, asec-pentyl group, a tert-pentyl group, a n-hexyl group, an isohexylgroup, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, anisoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octylgroup, an isooctyl group, a sec-octyl group, a tert-octyl group, ann-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group,an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decylgroup, and a C₁-C₁₀ alkoxy group, and r and s are each independently aninteger from 1 to 5 wherein, when r is 2 or greater, groups Q₁ are eachidentical to or different from each other, and when s is 2 or greater,groups Q₂ are each identical to or different from each other.
 5. Thelithium secondary battery of claim 1, wherein the piperazine derivativeof Formula 1 comprises at least one of compounds represented by Formulae3 to 6


6. The lithium secondary battery of claim 1, wherein the piperazinederivative is disposed on a surface of a cathode at an operating voltageof from about 4.0 V to about 5.5 V.
 7. The lithium secondary battery ofclaim 1, wherein the lithium salt comprises LiPF₆, LiBF₄, LiSbF₆,LiAsF₆, LiCF₃SO₃, Li(CF₃SO₂)₃C, Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiClO₄, LiAlO₄,LiAlCl₄, LiBPh₄, LiN(C_(x)F_(2x+1)SO₂)(C_(x)F_(2y+1)SO₂), wherein x andy are natural numbers, LiCl, Lil, lithium bisoxalato borate, or acombination thereof.
 8. The lithium secondary battery of claim 1,wherein an amount of the piperazine derivative additive is from about0.005 percent by weight to about 1 percent by weight based on a totalweight of the non-aqueous liquid electrolyte.
 9. The lithium secondarybattery of claim 1, wherein the cathode active material comprises atleast one of LiCoO₂, LiNi_(1−x)Co_(x)O₂ (wherein 0≦x<1), Li_(1−x)M_(x)O₂(wherein M comprises at least one of Mn and Fe, and 0.03<x<0.1),Li[Ni_(x)Co_(1−2x)Mn_(x)]O₂ (wherein 0<x<0.5), Li[Ni_(x)Mn_(x)]O₂(wherein 0<x≦0.5), Li_(1+x)(Ni,Co,Mn)_(1−y)O_(z)(wherein 0<x≦1, 0≦y<1and 2≦z≦4), LiM₂O₄ (wherein M comprises at least one of Ti, V, and Mn),LiM_(x)Mn_(2−x)O₄ (wherein M is a transition metal), LiFePO₄, LiMPO₄(wherein M comprises at least one of Mn, Co, and Ni), V₂O₅, V₂O₃,VO₂(B), V₆O₁₃, V₄O₉, V₃O₇, Ag₂V₄O₁₁, AgVO₃, LiV₃O₅, δ-Mn_(y)V₂O₅,δ-NH₄V₄O₁₀, Mn_(0.8)V₇O₁₆, LiV₃O₈, Cu_(x)V₂O₅, Cr_(x)V₆O₁₃, M₂(XO₄)₃(wherein M is a transition metal; and X comprises at least one of S, P,As, Mo, and W), and Li₃M₂(PO₄)₃ (wherein M comprises at least one of Fe,V, and Ti).
 10. The lithium secondary battery of claim 1, wherein thecathode active material comprises Li_(1+x)M_(1−x)O₂ (wherein M comprisesat least one of Ni, Co, and Mn, and 0.05≦x≦0.2), orLiNi_(0.5)Mn_(1.5)O₄.
 11. The lithium secondary battery of claim 1,wherein the anode active material comprises at least one of lithiummetal, a lithium metal alloy, a transition metal oxide, a material thatallows doping or undoping of lithium, and a material that allowsreversible intercalation and deintercalation of lithium ions.
 12. Thelithium secondary battery of claim 1, further comprising a separatordisposed between the cathode and the anode.
 13. The lithium secondarybattery of claim 1, wherein an amount of the piperazine derivativeadditive is from about 0.01 percent by weight to about 1 percent byweight based on a total weight of the non-aqueous liquid electrolyte.14. A non-aqueous liquid electrolyte for a lithium secondary battery,the non-aqueous liquid electrolyte comprising: a lithium salt; anon-aqueous organic solvent; and a piperazine derivative additiverepresented by Formula 1 having an oxidation potential lower than anoxidation potential of the non-aqueous organic solvent by about 2 V toabout 4 V:

wherein, in Formula 1, at least one of X and Y is selected from a C₁-C₆₀thioalkyl group, a C₁-C₆₀ hydroxyalkyl group, a C₁-C₆₀ alkylnitrilegroup, and a substituted C₆-C₆₀ aryl group, and the unselected rest of Xand Y is a hydrogen atom; R₁ to R₄ are each independently selected froma hydrogen atom, a deuterium atom, a halogen atom, a hydroxyl group, acyano group, a nitro group, an azido group, an amino group, an amidogroup, an amidino group, a hydrazine group, a hydrazone group, acarboxyl group or a salt thereof, a sulfonic acid group or a saltthereof, a phosphoric acid group or a salt thereof, a thiol group,—C(═O)—H, a substituted or unsubstituted C₁-C₆₀ alkyl group, asubstituted or unsubstituted C₁-C₆₀ alkoxy group, a substituted orunsubstituted C₁-C₆₀ heteroalkyl group, a substituted or unsubstitutedC₂-C₆₀ alkenyl group, a substituted or unsubstituted C₂-C₆₀ alkenylgroup, a substituted or unsubstituted C₃-C₁₀ cycloalkyl group, asubstituted or unsubstituted C₃-C₁₀ heterocycloalkyl group, asubstituted or unsubstituted C₂-C₁₀ cycloalkenyl group, a substituted orunsubstituted C₂-C₁₀ heterocycloalkenyl group, a substituted orunsubstituted C₆-C₆₀ aryl group, a substituted or unsubstituted C₆-C₆₀aryloxy group, a substituted or unsubstituted C₂-C₆₀ heteroaryl group,-(Q₁)_(r)-(Q₂)_(s), —N(Q₃)(Q₄)(Q₅), —P(═O)(Q₆)(Q₇), and—P(Q₈)(Q₉)(Q₁₀)(Q₁₁); wherein at least one of R₁₁ to R₁₄ and at leastone of R₂₁ to R₃₀ are optionally linked to each other to form asubstituted or unsubstituted, saturated or unsaturated ring; Q₁ is atleast one selected from —O—, —S—, —C(═O)—, a substituted orunsubstituted C₁-C₆₀ alkylene group, a substituted or unsubstitutedC₂-C₆₀ alkenylene group, a substituted or unsubstituted C₃-C₁₀cycloalkylene group, a substituted or unsubstituted C₃-C₁₀heterocycloalkylene group, a substituted or unsubstituted C₂-C₁₀cycloalkenylene group, a substituted or unsubstituted C₂-C₁₀heterocycloalkenylene group, a substituted or unsubstituted C₆-C₆₀arylene group, and a substituted or unsubstituted C₂-C₆₀ heteroarylenegroup; Q₂ to Q₁₁ are each independently selected from a deuterium atom,a halogen atom, a hydroxyl group, a cyano group, a nitro group, an azidogroup, an amino group, an amido group, an amidino group, a hydrazinegroup, a hydrazone group, a carboxyl group or a salt thereof, a sulfonicacid group or a salt thereof, a phosphoric acid group or a salt thereof,a thiol group, a substituted or unsubstituted C₁-C₆₀ alkyl group, asubstituted or unsubstituted C₁-C₆₀ alkoxy group, a substituted orunsubstituted C₁-C₆₀ heteroalkyl group, a substituted or unsubstitutedC₂-C₆₀ alkenyl group, a substituted or unsubstituted C₂-C₆₀ alkynylgroup, a substituted or unsubstituted C₁-C₆₀ alkoxy group, a substitutedor unsubstituted C₃-C₁₀ cycloalkyl group, a substituted or unsubstitutedC₃-C₁₀ heterocycloalkyl group, a substituted or unsubstituted C₂-C₁₀cycloalkenyl group, a substituted or unsubstituted C₂-C₁₀heterocycloalkenyl group, a substituted or unsubstituted C₆-C₆₀ arylgroup, a substituted or unsubstituted C₆-C₆₀ aryloxy group, and asubstituted or unsubstituted C₂-C₆₀ heteroaryl group; and r and s areeach independently an integer from 1 to 5, wherein, when r is 2 orgreater, groups Q₁ are each identical to or different from each other,and when s is 2 or greater, groups Q₂ are each identical to or differentfrom each other.